This invention generally relates to the fabrication of electrical interconnectors used to electrically connect printed circuit boards and other electrical components in a vertical or z-axis direction to form three-dimensional electronic modules. More particularly, the present invention relates to a new and improved machine and method for fabricating z-axis interconnectors of the type formed from helically coiled strands of wire, in which at least one longitudinal segment of the coiled strands is untwisted in an anti-helical direction to expand the strands of wire into a resilient bulge. Bulges of the interconnector are then inserted into vias of vertically stacked printed circuit boards to establish an electrical connection through the z-axis interconnector between the printed circuit boards of the three dimensional module.
The evolution of computer and electronic systems has demanded ever-increasing levels of performance. In most regards, the increased performance has been achieved by electronic components of ever-decreasing physical size. The diminished size itself has been responsible for some level of increased performance because of the reduced lengths of the paths through which the signals must travel between separate components of the systems. Reduced length signal paths allow the electronic components to switch at higher frequencies and reduce the latency of the signal conduction through relatively longer paths. One technique of reducing the size of the electronic components is to condense or diminish the space between the electronic components. Diminished size also allows more components to be included in a system, which is another technique of achieving increased performance because of the increased number of components.
One particularly effective approach to condensing the size between electronic components is to attach multiple semiconductor integrated circuits or xe2x80x9cchipsxe2x80x9d on printed circuit boards, and then stack multiple printed circuit boards to form a three-dimensional configuration or module. Electrical interconnectors are then extended vertically, in the z-axis dimension, between the printed circuit boards which are oriented in the horizontal x-axis and y-axis dimensions. The z-axis interconnectors, in conjunction with conductor traces of each printed circuit board, connect the chips of the module with short signal paths for efficient functionality. The relatively high concentration of chips, which are connected by the three-dimensional, relatively short length signal paths, are capable of achieving very high levels of functionality.
The vertical electrical connections between the stacked printed circuit boards are established by using z-axis interconnectors. Z-axis interconnectors contact and extend through plated through holes or xe2x80x9cviasxe2x80x9d formed in each of the printed circuit boards. The chips of each printed circuit board are connected to the vias by conductor traces formed on or within each printed circuit board. The vias are formed in each individual printed circuit board of the three-dimensional modules at the same locations, so that when the printed circuit boards are stacked in the three-dimensional module, the vias of all of the printed circuit boards are aligned vertically in the z-axis. The z-axis interconnectors are then inserted vertically through the aligned vias to establish an electrical contact and connection between the vertically oriented vias of each module.
Because of differences between the individual chips on each printed circuit board and the necessity to electrically interconnect to the chips of each module in a three-dimensional sense, it is not always required that the z-axis interconnectors electrically connect to the vias of each printed circuit board. Instead, those vias on those circuit boards for which no electrical connection is desired are not connected to the traces of that printed circuit board. In other words, the via is formed but not connected to any of the components on that printed circuit board. When the z-axis interconnector is inserted through such a via, a mechanical connection is established, but no electrical connection to the other components of the printed circuit board is made. Alternatively, each of the z-axis interconnectors may have the capability of selectively contacting or not contacting each via through which the interconnector extends. Not contacting a via results in no electrical connection at that via. Of course, no mechanical connection exists at that via either, in this example.
A number of different types of z-axis interconnectors have been proposed. One particularly advantageous type of z-axis interconnector is known as a xe2x80x9ctwist pin.xe2x80x9d Twist pin z-axis interconnectors are described in U.S. Pat. Nos. 5,014,419, 5,064,192, and 5,112,232, all of which are assigned to the assignee hereof.
An example of a prior art twist pin 50 is shown in FIG. 1. The twist pin 50 is formed from a length of wire 52 which has been formed conventionally by helically coiling a number of outer strands 54 around a center core strand 56 in a planetary manner, as shown in FIG. 2. At selected positions along the length of the wire 52, a bulge 58 is formed by untwisting the outer strands 54 in a reverse or anti-helical direction. As a result of untwisting the strands 54 in the anti-helical direction, the space consumed by the outer strands 54 increases, causing the outer strands 54 to bend or expand outward from the center strand 56 and create a larger diameter for the bulge 58 than the diameter of the regular stranded wire 52. The laterally outward extent of the bulge 58 is illustrated in FIG. 3, compared to FIG. 2.
The strands 54 and 56 of the wire 52 are preferably formed from beryllium copper. The beryllium copper provides necessary mechanical characteristics to maintain the shape of the wire in the stranded configuration, to allow the outer strands 54 to bend outward at each bulge 58 when untwisted, and to cause the bulges 58 to apply resilient radial contact force on the vias of the printed circuit boards. To facilitate and enhance these mechanical properties, the twist pin will typically be heat treated after it has been fabricated. Heat treating anneals or hardens the beryllium copper slightly and tempers the strands 54 at the bulges 58, causing enhanced resiliency or spring-like characteristics. It is also typical to plate the fabricated twist pin with an outer coating of gold. The gold plating establishes a good electrical connection with the vias. To cause the gold-plated exterior coating to adhere to the twist pin 50, usually the beryllium copper is first plated with a layer of nickel, and the gold is plated on top of the nickel layer. The nickel layer adheres very well to the beryllium copper, and the gold adheres very well to the nickel.
The bulges 58 are positioned at selected predetermined distances along the length of the wire 52 to contact the vias 60 in printed circuit boards 62 of a three-dimensional module 64, as shown in FIG. 4. Contact of the bulge 58 with the vias 60 is established by pulling the twist pin 50 through an aligned vertical column of vias 60 in the module 64. The outer strands 54 of the wire 52 have sufficient resiliency when deflected into the outward protruding bulge 58, to resiliently press against an inner surface of a sidewall 66 of each via 60, and thereby establish the electrical connection between the twist pin 50 and the via 60, as shown in FIG. 5. In those circumstances where an electrical connection is not desired between the twist pin 50 and the components of a printed circuit board, the via 60 is formed but no conductive traces connect the via to the other components of the printed circuit board. One such via 60xe2x80x2 is shown in FIG. 4. The sidewall 66 of the via 60xe2x80x2 extends through the printed circuit board, but the via 60xe2x80x2 is electrically isolated from the other components on that printed circuit board because no traces extend beyond the sidewall 66. Inserting a bulge 58 of the twist pin 50 into a via 60xe2x80x2 that is not connected to the other components of a printed circuit board eliminates an electrical connection from that twist pin to that printed circuit board, but establishes a mechanical connection between the twist pin and the printed circuit board which helps support and hold the printed circuit board in the three-dimensional module.
To insert the twist pins 50 into the vertically aligned vias 60 of the module 64 with the bulges 58 contacting the inner surfaces 66 of the vias 60, a leader 68 of the regularly-coiled strands 54 and 56 extends at one end of the twist pin 50. The strands 54 and 56 at a terminal end 70 of the leader 68 have been welded or fused together to form a rounded end configuration 70 to facilitate insertion of the twist pin 50 through the column of vertically aligned vias. The leader 68 is of sufficient length to extend through all of the vertically aligned vias 60 of the assembled stacked printed circuit boards 62, before the first bulge 58 makes contact with the outermost via 60 of the outermost printed circuit board 62. The leader 68 is gripped and the twist pin 50 is pulled through the vertically aligned vias 60 until the bulges 58 are aligned and in contact with the vias 60 of the stacked printed circuit boards. To position the bulges in contact with the vertically aligned vias, the leading bulges 58 will be pulled into and out of some of the vertically aligned vias until the twist pin 50 arrives at its final desired location. The resiliency of the strands 54 allow the bulges 58 to move in and out of the vias without losing their ability to make sound electrical contact with the sidewall of the final desired via into which the bulges 58 are positioned. Once appropriately positioned, the leader 68 is cut off so that the finished length of the twist pin 50 is approximately at the same level or slightly beyond the outer surface of the outer printed circuit board of the module 64. A tail 72 at the other end of the twist pin 50 extends a shorter distance beyond the last bulge 58. The strands 54 and 56 at an end 74 of the tail 72 are also fused together. The length of the tail 72 positions the end 74 at a similar position to the location where the leader 68 was cut on the opposite side of the module. However, if desired, the length of the tail 72 or the remaining length of the leader 68 after it was cut may be made longer or shorter. Allowing the tail 72 and the remaining portion of the leader 68 to extend slightly beyond the outer printed circuit boards 62 of the module 64 facilitates gripping the twist pin 50 when removing it from the module 64 to repair or replace any defective components. In those circumstances where it is preferred that the ends of the twist pin do not extend beyond the outside edges of the three-dimensional module, an overlay may be attached to the outermost printed circuit boards to make the ends of the twist pin flush with the overlay.
The ability to achieve good electrical connections between the vias 60 of the printed circuit boards depends on the ability to precisely position the location of the bulges 58 along the length of wire 52. Otherwise, the bulges 58 would be misaligned relative to the position of the vias, and possibly not create an adequate electrical connection. Therefore, it is important in the formation of the twist pins 50 that the bulges 58 be separated by predetermined intervals 76 (FIG. 1) along the length of the wire 52. The position of the bulges 58 and the length of the intervals 76 depend on the desired spacing between the printed circuit boards 62 of the module 64. The amount of bending of each of the outer conductors 54 at each bulge 58 must also be controlled so that each of the bulges 58 exercises enough force to make good electrical contact with the vias. Moreover, the amount of outward deflection or bulging of each of the bulges 58 must be approximately uniform so that none of the bulges 58 experiences permanent deformation when the bulge is pulled through the vias. Distortion-induced disparities in the dimensions of the bulges adversely affect their ability to make sound electrical connections with the vias 60. Further still, each twist pin 50 should retain a coaxial configuration along its length without slight angular bends at each bulge and without any bulge having asymmetrical characteristics. The coaxial configuration facilitates inserting the twist pin through the vertically aligned vias, maintaining the resiliency of the bulges, and establishing good electrical contact with the vias.
The requirements for close tolerances and precision in the twist pins are made more significant upon recognizing the very small size of the twist pins. The typical sizes of the most common sizes of helically-coiled wire are about 0.0016, 0.0033 and 0.0050 in. in diameter. The diameters of the strands 54 and 56 used in forming these three sizes of wires are 0.005, 0.0010, and 0.0015 in., respectively: The typical length of a twist pin having four to six bulges which extends through four to six printed circuit boards will be about 1 to 1.5 inches. The outer diameter of each bulge 58 will be approximately two to three times the diameter of the regularly stranded wire in the intervals 76. The tolerance for locating the bulges 58 between intervals 76 is in the neighborhood of 0.002 in. The weight of a typical four-bulge twist pin is about 0.0077 grams, making it so light that handling the twist pin is very difficult. Handling each twist pin is also complicated because its small dimensions do not easily resist the forces that are necessary to manually manipulate the twist pin without bending or deforming it. It is not unusual that a complex 4 in.xc3x974 in. module 64 may require the use of as many as 22,000 twist pins. Thus, the relatively large number of twist pins necessary to assemble each three-dimensional module require an ability to fabricate a relatively large number of the twist pins in an efficient and rapid manner.
A general technique for fabricating twist pins is described in the three previously-identified U.S. patents. That described technique involves advancing the length of the stranded wire, clamping the stranded wire above and below the location where the bulge is to be formed, fusing the outer strands of the wire to the core strand of the wire preferably by laser welding at the locations above and below the bulge, and rotating the wire between the two clamps in an anti-helical direction to form the bulge.
In a prior art implementation of this twist pin fabrication technique, a wire feeder advanced an end of the helically stranded wire which was wound on a spool. The wire feeder employed a lead screw mechanism driven by an electric motor to advance the wire and unwind it from the spool. A solenoid-controlled clamp was connected to the lead screw mechanism to grip the wire as the lead screw mechanism advanced as much of the stranded wire from the spool as was necessary for use at each stage of fabrication of the twist pin. To advance more wire, the clamp opened and the lead screw mechanism retracted in a reverse movement. The clamp then closed again on the wire and the electric motor again advanced the lead screw mechanism.
While this prior art wire feeder mechanism was functional, the reciprocating movement of the feeder mechanism reduced efficiency and slowed the speed of operation. Half of the reciprocating movement, the return movement to the beginning position, was wasted motion. Moreover, the relatively high inertia and mass of the lead screw, clamp and motor armature required extra force and hence time to execute the reversing movements necessary for reciprocation. Furthermore, the rotational mass of the wire wound on the spool limited the acceleration rate at which the lead screw could unwind the wire off of the spool. The rotational mass was frequently sufficient enough to cause the wire to slip in the clamp carried by the lead screw. Slippage at this location resulted in the formation of the bulges at incorrect positions and incorrect lengths of the leader 68 and the internal lengths 76. The desire to avoid slippage also limited the operating speed of the fabricating equipment.
The prior art bulge forming mechanism included two clamping devices which closed on the wire above and below at the location where each bulge was to be formed. The clamping devices held a wire while a laser beam fused the outer strands 54 to the center core strand 56 at those locations. Thereafter, the lower clamping device was rotated in an anti-helical direction while the upper clamping device held the wire stationary, thereby forming the bulge 58.
The lower clamping device was carried by a sprocket, and the wire extended through a hole in the center of the sprocket. A first pneumatic cylinder was connected to the clamping device to cause the clamping device to grip the wire. A chain extended around the sprocket and meshed with the teeth of the sprocket. One end of the chain was connected to a spring, and the other end of the chain was connected to a second pneumatic cylinder. When the second pneumatic cylinder was actuated, its rod and piston pulled the chain to rotate the sprocket by the amount of the piston throw. Upon reaching the end of its throw, the rod and cylinder of the second pneumatic cylinder was returned in the opposite direction to its original position by the force of the spring which pulled the chain in the opposite direction. Of course, moving the chain to its original position also rotated the sprocket in the opposite direction to its original position.
After gripping the wire by activating the first pneumatic cylinder, the second pneumatic cylinder was activated to rotate the sprocket in the anti-helical direction. However, the throw of the second pneumatic cylinder, and the amount of rotation of the sprocket, was insufficient to completely form a bulge with a single rotational movement. Instead, two of separate rotational movements were required to completely form the bulge. After the rotation, the lower clamping device released its grip on the wire while the sprocket rotated in the reverse direction. Upon rotating back to the initial position again, the lower clamping device again gripped the wire and another rotational movement of the sprocket and gripping device was executed to finish forming the bulge.
By providing only a limited amount of rotational movement so as to require two rotations to form the bulge, a significant amount of time was consumed in forming each bulge. The latency of reversing the movement of the components and executing multiple bulge forming movements slowed the fabrication rate of the twist pins. The rotational mass of the sprocket and the clamping mechanism with its attached solenoid activation clamping device reduced the rate at which these elements could be accelerated, and also constituted a limitation on the speed at which twist pins could be fabricated. Apart from the rotational mass issues, acceleration had to be limited to avoid inducing wire slippage. The need to reverse the direction of movement of numerous reciprocating components limited the rate at which the twist pins bulges could be fabricated.
After formation of the bulges in the prior art twist pin fabricating machine, the wire with the formed bulges was cut to length to form the twist pin. The leader of the twist pin extended into a venturi through which gas flowed. The effect of the gas flowing through the venturi was to induce a slight tension force on the wire, and hold it while a laser beam severed the wire at the desired length. The laser beam fused the ends 70 and 74 of the strands 54 and 56 as it severed the fabricated twist pin from the length of wire. The tension force induced on the wire by the gas flowing through the venturi propelled the twist pins into a random pile called a xe2x80x9chaystack.xe2x80x9d After a sufficient number of twist pins had accumulated, they were placed into a separate sorting and singulating machine which ultimately delivered the twist pins one at a time in a specific orientation into a carrier. The pins were later heat treated and transferred from the carrier and inserted into the three-dimensional modules.
The process of sorting the twist pins, orienting them, delivering them into the carrier, and making sure that the twist pins were received properly within the carrier required considerable human intervention and machine handling after the twist pins were fabricated. Occasionally the twist pins would be lodged in tubes which guided the twist pins into the carrier by an air flow. Delivering the twist pins into the receptacles in the carrier was also difficult, and human intervention was required to assure that the twist pins were properly received in the receptacles. Twist pin sorting also occasionally resulted in jamming and bending the twist pins. In general, the post-fabrication processing steps required to organize the twist pins for their subsequent use contributed to overall inefficiency.
These and other considerations pertinent to the fabrication of twist pins have given rise to the new and improved aspects of the present invention.
One improved aspect of the present invention involves withdrawing wire from a source, such as a spool, and advancing that wire to be used in fabricating twist pins in the such a manner that twist pins can be more rapidly and more efficiently fabricated compared to previous techniques. Another improved aspect of the present invention involves fabricating twist pins having more uniform and precisely controlled characteristics, such as more precisely positioned bulges and leaders, tails and intervals of more precisely controlled dimensions. Another improved aspect of the present invention involves feeding the wire and fabricating twist pins without using reciprocal motions. The lost motion of return strokes and the latency associated with reciprocation decreases the speed of fabricating the twist pins. The necessity to accelerate relatively massive components is avoided by using continuous movements or intermittent movements which do not involve changes of direction and which tend to conserve energy and momentum without requiring acceleration of massive components. Another improved aspect is that the nature of the movements involved does not tend to induce slippage of the wire during the fabrication of the twist pin. Other aspects of the present invention allow the constituent components of the twist pin to be more precisely fabricated into the desired shapes, dimensions and tolerances, while still allowing twist pins of different sizes to be fabricated.
In one principal regard, the present invention involves a wire feed mechanism for receiving wire from a wire source and advancing the wire to be used as an electrical connector. The wire feed mechanism comprises a cavity within which to receive wire from the source, a wire-supplying device which supplies wire from the source into the cavity and maintains an amount of slack wire within the cavity, and a wire-advancing device which withdraws a predetermined amount of the slack wire from the cavity and advances that predetermined amount of wire to be used for the electrical connector.
In another principal regard, the present invention involves a wire feed mechanism for receiving wire from a source and advancing the wire to be used as an electrical connector. In this instance, the wire feed mechanism comprises a cavity within which to receive wire from the source, a wire-supplying device which supplies wire from the source into the cavity, a sensor located in the cavity to sense a predetermined amount of slack wire within the cavity, and a controller responsive to the sensor to control the supply of additional wire from the source into the cavity to establish and maintain the predetermined slack amount of wire within the cavity.
In yet another principal regard, the present invention involves a method of withdrawing wire from a wire source and advancing the withdrawn wire for use as an electrical connector. The method comprises the steps of withdrawing a sufficient amount of wire from the wire source to form a predetermined length of slack wire, configuring the slack wire into a predetermined configuration, advancing slack wire from the predetermined configuration for use as the electrical connector, and supplying additional wire from the wire source to compensate for the slack wire advanced from the predetermined configuration to maintain the predetermined configuration of slack wire.
Certain preferred aspects of the invention involve advancing the slack wire from the cavity in predetermined interval lengths and limiting the length of an interval to an amount of wire less than the amount of slack wire in the cavity. Preferably, the additional wire from the source is applied to the cavity at a faster rate than the slack wire is advanced from the predetermined configuration within the cavity. The wire is supplied to the cavity independently of advancing the wire from the cavity. The mass and inertia effects of withdrawing the wire from the wire source are isolated by the slack wire within the cavity from the mass and inertia effects associated with advancing the slack wire from the cavity. Slippage is avoided because the advancement of the wire needs only to overcome the considerably reduced mass and inertia effects of the slack wire in the cavity, rather than to overcome the considerably greater mass and inertia effects of withdrawing the wire from the source. This is particularly the case when the wire source is a spool upon which the wire has been wound, and to unwind the wire from the spool requires that the entire mass of wire wound on the spool be rotated.
Other preferred aspects of the present invention involve sensing a characteristic of the slack wire configuration to maintain the slack wire in the configuration. Preferably the slack wire configuration involves bending the wire within the cavity into at least one curve, and more preferably into an S-shaped configuration having two curves. The amount of wire supplied, the amount of withdrawn wire advanced and the dimensions of the cavity limit the curvature of each man in the wire to avoid permanently set or deforming the wire. A characteristic, such as the position, of at least one and preferably both of the curves is sensed, and the additional wire is supplied in response. For example, bar-type position sensors may be used to determine the contact of the curved wire. If the two curves of wire in the S-shaped configuration do not contact the bar-type sensors, additional wire is supplied until the amount of slack wire in the cavity widens the S-shaped configuration to place the curves in contact with the sensors. The S-shaped configuration is thereby maintained even while advancing the slack wire from the S-shaped configuration.
The additional wire is preferably supplied by roller that makes frictional contact with the wire from the source. A motor rotates the roller to avoid inefficient, time-consuming and problematic reciprocating movements. The motor driving the wire-supplying roller is preferably a conventional direct-current (DC) motor which is driven by a power control signal. The power control signal preferably has a repeating duty cycle characteristic defining an on-time during which power is supplied and an off-time during which power is not supplied. A speed reducing gear head may connect the motor to the roller. Using a power control signal with a duty cycle characteristic to energize the motor allows close control over the wire advanced because of the ability to control and avoid rotational inertia or wind-down effects. Consequently, an excessive amount of additional wire is not supplied into the cavity, but only a sufficient amount is supplied to maintain the predetermined configuration.
The wire is preferably advanced from the cavity by a spindle which is positioned in frictional contact with the wire and which is rotated by a spindle drive motor. Preferably the spindle drive motor is a stepper motor which allows a precise and fine resolution of wire to be advanced from the cavity by electronically controlling the number of energizing pulses supplied to the drive motor. Precise advancement of the wire is desirable because the advancement of the wire locates the position at which the characteristics of the electrical connector, such as the bulges on a twist pin, are formed.
The present invention is preferably used in cooperation with fabricating an electrical connector having bulges formed in a wire formed from helically coiled strands. The wire is gripped and rotated in an anti-helical direction to untwist the strands and form the bulge. The advancement of the wire locates the position where the bulges formed. The advancement of the wire also locates the position where the wire is to be severed to separate a segment of the wire having the bulges from the remaining wire, thereby completing the fabrication of the twist pin.
By separately uncoiling the wire from the spool to form the slack wire configuration and then advancing the wire from the slack wire to form the connector, the mass and rotational inertia effects twist pin electrical conductors can be manufactured more rapidly and efficiently. The position of the bulges another characteristics of the twist pin are more uniformly established, because wire slippage is less likely when advancing the wire from the amount of slack wire. The wire supplied from the spool and advanced by separately controlled actions which do not involve the inefficiency and latency associated with reciprocal actions. The lost motion of return strokes and the latency associated with reciprocation decreases the speed of fabricating the twist pins. Using rollers and spindle is to advance the wire avoids the necessity to accelerate and decelerate relatively massive components.
A more complete appreciation of the present invention and its scope may be obtained from the accompanying drawings, which are briefly summarized below, from the following detailed descriptions of presently preferred embodiments of the invention, and from the appended claims.